The present invention relates to a bearing of an axial air gap type electric motor, and more particularly, relates to a preventing structure of a vibration and noises of the bearing using a radial ball bearing.
A structure for removing a play space of an inner ring and an outer ring of the ball bearing has been used as a structure for preventing a vibration and noises of the bearing using the ball bearing in the related art. Namely, this structure is a structure for arranging a pre-pressurizing means for pre-pressurizing the outer ring side to intentionally shift the inner ring and the outer ring of the ball bearing in the direction of a rotating axis.
For example, this structure will be explained by using the radial gap type electric motor shown in FIG. 13.
In the sectional view of FIG. 13, reference numerals 81, 82 and 83 respectively designate a rotating shaft of a motor, a rotor and a stator wound by a wire. Reference numerals 84, 85 and 86 respectively designate a bracket of a side opposed to load, a bracket of the load side, and a frame. Reference numerals 87, 88 and 89 respectively designate a double row angular ball bearing, a ball bearing and a pressing plate. Reference numerals 90, 91 and 92 respectively designate a waveform spring (pre-pressurizing section) of an elastic body, an optical type encoder of a separating type, and an oil seal.
The radial gap type electric motor will next be explained with an assembly method as a center. In the rotor 82, magnets of an outer circumference are alternately magnetized to the N-poles and the S-poles in advance, and are press-fitted and fixed to the rotating shaft 81. The stator 83 is shrink-fitted and fixed to the frame 86.
Next, inner rings of the double row angular ball bearing 87 and the ball bearing 88 are press-fitted and fixed to predetermined positions of the rotating shaft 81. An outer ring of the double row angular ball bearing 87 is stored to a housing portion of the bracket 84, and is screwed and fixed to the bracket 84 so as to be nipped by the housing portion and the pressing plate 89. The bracket 84 of this state is fixed to an opening end portion of the side opposed to the load in the frame 86. Further, the opening end portion of the opposite (load) side of the frame 86 and the bracket 85 are fitted such that the outer ring of the ball bearing 88 and the waveform spring 90 are abutted within the housing of the bracket 85.
When the bracket 85 and the frame 86 are fixed, the outer ring of the ball bearing 88 is coated with an adhesive, and the waveform spring 90 is compressed by a size corresponding to an appropriate given pressure in an axial direction, and is fixed. Namely, in this motor, all the inner and outer rings of the double row angular ball bearing 87 and the ball bearing 88 are fixed in a state in which the appropriate given pressure is applied (e.g., see patent literature 1).
Further, an example for applying the bearing structure having such a pre-pressurizing section to the axial air gap type electric motor will be explained.
As shown in the cross-sectional view of the electric motor of FIG. 11 and the plan view of a stator core of FIG. 12, the axial air gap type electric motor of three phases and nine slots includes a stator 20 approximately formed in a disk shape, and rotors 31, 32 constructed by a pair of plastic magnets oppositely arranged with a predetermined air gap on both sides of the stator 20. The rotors 31, 32 commonly have the same rotating shaft 24. The stator 20 has a bearing portion 26 for supporting the rotating shaft 24 on its inner circumferential side.
In reality, the stator 20 and the rotors 31, 32 are stored into an unillustrated bracket (box body), and an outer circumferential side of the stator 20 is fixed to a bracket.
The stator 20 has a stator core 25 formed in a ring shape (a so-called donut shape), and a bearing portion 26. coaxially inserted on an inner circumferential side of the stator core 25. The stator core 25 is integrally molded by synthetic resin 21. In this example, each bearing 26 has one radial ball bearing.
As shown in FIG. 12, the stator core 25 is constructed by connecting nine ball members 25a to 25i in a ring shape. All the respective ball members 25a to 25i have the same shape.
Further, as shown in FIG. 11, one ball member 25d has a tease (iron core) 51 formed by laminating plural metallic plates in a trapezoidal shape. An insulator 50 constructed by synthetic resin is integrally formed around the tease 51 except for its both side faces.
The insulator 50 is entirely formed in a bobbin shape of an H-shape in section including flanges 52, 53 of an approximately fan shape arranged as a pair of left and right along both the side faces of the tease 51. A coil 27 is structurally wound between these flanges 52, 53.
After a ball member unit of three phases is formed, as shown in FIG. 12, a ball member for a U-phase is sequentially arranged in an arc shape. In this case, a ball member for a V-phase adjacent to the ball member for the U-phase and a ball member for a W-phase adjacent to the ball member for the V-phase are respectively arranged in an arc shape. Both neighbors of these respective ball members are connected to each other. Thus, the nine ball members are assembled in a ring shape.
Ua, Ub are leader lines for the U-phase, and Va, Vb are leader lines for the V-phase, and Wa, Wb are leader lines for the W-phase. Each leader line is connected to a driving circuit substrate for an unillustrated electric motor through a holding body 30 of a resin property for holding to the stator core 25.
An outer circumferential portion and an inner circumferential portion of each ball member, and the holding body 30 for the leader line are solidified by synthetic resin 21 by insert molding. Thereafter, the rotating shaft 24 fixing the bearing portion 26 thereto in one predetermined position is inserted from one face of the stator core 25 into its center. Further, this bearing portion 26 is press-fitted into the stator core 25.
Next, a leaf spring of a ring shape of a waveform in section (wave washer spring) 33 is arranged between the inner circumferential side of the other face of the stator core 25 and the bearing portion 26. Next, another bearing portion 26 is inserted from the other direction of the rotating shaft 24, and is fixed in a predetermined position of the rotating shaft 24 (e.g., see patent literature 2).
However, in the above two conventional examples, the radial ball bearing is used in the bearing. Therefore, a space of play exists in these inner and outer rings, and resonance is generated by a sliding period of a rotating axis direction generated by attraction and repulsion of the rotor due to magnetic force, and the value of a repulsion constant of the leaf spring for pre-pressurizing the outer ring. Thus, there is a case in which large vibration and noises are generated. The principle of this resonance will be explained in detail in embodiments.    [Patent literature 1] JP-A-2003-161328 (pages 3 to 4 and FIG. 1)    [Patent literature 2] JP-A-2004-282989 (pages 9 to 12 and FIG. 1).